The present invention relates generally to gas burner apparatus and, in a preferred embodiment thereof, more particularly provides uniquely configured flashback resistant infrared gas burner apparatus representatively incorporated in the frypot heating system of a deep fat cooking fryer.
Gas fired infrared burners are well known heating elements and are utilized in a variety of heating applications such as space heating in commercial and industrial establishments and as burners used to supply heat to commercial cooking equipment such as deep fat fryers. Burners of this general type typically comprise a rectangular metal housing having an open side within which one or more foranimous ceramic burner plates are suitably retained. Extending inwardly through a front end wall of the burner housing is a supply pipe which flows a suitable airgaseous fuel mixture into the housing interior. The pipe has an open inner end positioned within a rear end portion of the housing.
During startup of the burner, the air-fuel mixture discharged from the supply pipe begins to fill the burner housing, from the rear end of its housing toward the front end thereof, and is flowed outwardly through the perforations in the foranimous burner plate structure, the air-fuel mixture outflow beginning at the rearmost perforations and spreading to the frontmost perforations as the housing interior fills with the air-fuel mixture in a rear-to-front direction. When the forwardly spreading air-fuel mixture outflow reaches the front end of the outer side surface of the plate structure, an igniter positioned adjacent thereto ignites the air-fuel mixture to create and maintain a flame along essentially the entire exterior surface of the foranimous plate structure.
Particularly when the burner is incorporated in other heating equipment, such as the frypot section of a deep fat cooking fryer, it is necessary for access purposes to position the igniter adjacent the front or inlet end of the burner as just described. Coupled with the rearward pre-startup spread of the air-fuel mixture within the burner housing and across the exterior side surface of the foranimous plate structure, this necessary forward positioning of the igniter has heretofore created two interrelated burner startup problems--"hard" ignition and "flashback".
The hard ignition problem arises due to the often considerable volume of air-fuel mixture which is discharged from the plate structure before the discharged mixture spreads forwardly to the front-mounted igniter. Upon reaching the igniter the entire volume of discharged air-fuel mixture built up along the exterior side surface of the plate structure is rapidly ignited causing a minor (though potentially harmful) external explosion along the plate structure. The amount of burner damage this hard ignition can cause is increased in situations (such as in frypot heating applications) where the air-fuel mixture is discharged from the plate structure into and partially fills an enclosed heating passage prior to this "delayed" ignition.
Flashback occurs when the exterior burner flame travels inwardly through the burner plate perforations and undesirably ignites the air-fuel mixture within the burner housing, thereby causing an extremely rapid pressure rise therein which can cause considerable damage to the housing and its foranimous plate structure. To inhibit such flashback the perforations in the plate structure are normally sized to provide the air-fuel mixture with an outflow velocity through such perforations which is equal to or just slightly greater than the inward flame spread velocity of the burning mixture on the outer side of the plate structure. However, despite this precaution, a sufficiently "hard" ignition (particularly within a confined area such as a heating flow passage) can rapidly drive the resulting flame inwardly through the plate perforations and cause flashback.
The possibility of both hard ignition and flashback in conventional infrared burners of the conventional type just described is significantly enhanced when, as in the case of many underdeveloped countries, natural gas is unavailable as a fuel source and "manufactured" gas must be used to fire the burner. Because of the much greater flame spread velocity associated with, for example, naptha-based manufactured gas (compared to that of natural gas), both the hard ignition and associated flashback phenomenons tend to be considerably more forceful and therefore potentially more damaging to the overall burner structure.
In view of the foregoing it is a primary object of the present invention to provide an improved gas fired infrared burner in which the above-mentioned hard ignition and flashback problems are eliminated or at least very substantially reduced.